In many types of control and measuring apparatuses it is necessary to determine with considerable accuracy the amount of liquid flowing through a conduit or tube at a given instant. Examples of such applications can be found in medicine where the amount of fluid injected intravenously into a patient must be given at a metered rate, or the amount of gasoline consumption in an automobile at any given time for any speed or any given acceleration, or the amount of cooling air flowing through a conduit containing communication carrying wires which must be maintained within some predetermined temperature range.
A specific example of the prior art is shown in U.S. Pat. No. 4,007,628 to WORCESTER which shows a flow meter having a reservoir divided into first and second compartments with the fluid (or air) entering the first compartment and passing into the second compartment through a first orifice in a rigid member separating the first and second compartments. The second compartment is in turn divided into first and second sub-compartments separated by a flexible diaphragm which flexes in accordance with the amount of air flowing into the second compartment of the main receptacle from the first compartment. The diaphragm is attached to a first cylinder which extends downwardly into a second cylinder secured within the first compartment with its top end terminated and sealed at the edges of a second orifice formed in the rigid element separating the first and second compartments. At the bottom of the first cylinder is a third orifice through which extends a tapered element secured at the bottom of the second cylinder. As the volume of air increases the flexible diaphragm is flexed upwardly pulling the first cylinder also in the upward direction and moving the orifice at the bottom thereof towards the diverging end of the tapered element secured within the second cylinder, thereby increasing the annular opening between the tapered element and the orifice at the bottom of the first cylinder and permitting more air to pass downwardly between the first and second cylinders and then upwardly through the annular opening at the bottom of the first cylinder and then into the second sub-compartment of the second compartment of the main receptacle and finally out the output conduit of the system. A wedge shaped device is attached to the first cylinder and is constructed to pass varying amounts of light, which emanate from a fixed light source secured at the bottom of the second cylinder, therethrough as the first cylinder rises in response to more air passing through the system. The light passed through the wedge is detected by a light responsive device on the other side of the wedge where it is converted into electrical signals which are utilized in some suitable manner.
Another example of a prior art fluid flow meter is shown in U.S. Pat. No. 3,776,036 by TAYLOR. A float is mounted in the incoming pipeline or conduit and has a flat tail piece formed at the opposite end thereof with a cut-out portion in such tail piece. The float is mounted on a cantilever spring and moves in the direction of flow of the fluid in proportion to the pressure and therefore the amount of fluid flow. A light source is mounted on one side of the tail piece and a light detector means is located on the other side of the tail piece in such a manner that as the fluid flow rate increases a greater amount of the cut out portion of the tail piece will be moved into position between the light source and the light detector means. Thus, the amount of light detected is proportional to the movement of the float and consequently to the amount of fluid flow in the pipeline.
Still another example of the prior art is shown in U.S. Pat. No. 4,297,899 to BLANEY et al. In this relatively complex structure the fluid flow measuring device includes a flexible diaphragm element which has as part of its assembly an orifice which moves along a tapered element securely fixed within the structure independently of the moving diaphragm. As the fluid flow increases the orifice moves towards the converging end of the tapered element and permits more fluid to flow through the annular opening created between the tapered element and the orifice. The flexible diaphragm and the orifice are also attached to a shaft which forms a central core member of a differential transformer and which moves within said differential transformer to vary the electrical output thereof. There is a known relationship between the output of the differential transformer and the rate of fluid flow.
A primary object of the present invention is to provide a device which measures the rate of flow of fluid in the tube and which is relatively simple and inexpensive to construct.
Another object of the invention is to provide a fluid flow meter which is relatively simple and inexpensive to construct but yet provides a high reliability of performance.
A third object is to provide a device which can measure the rate of flow of gas or fluid, which can be either transparent or transulucent, with a high degree of accuracy.
A fourth object is to provide a fluid flow meter which measures the instantaneous rate of flow of fluid through a tube with a high degree of reliability and accuracy and which does not impede the flow of fluid.
A fifth object of the invention is the improvement generally of devices for measuring the amount and rate of flow of fluid in a tube.